De-oiler system for an aeroengine

ABSTRACT

The invention relates to a de-oiler system for an aeroengine including a casing defining a volume containing a rotary shaft and a mixture of air and oil for processing. 
     The system comprises: 
     a hollow rotary tube; a de-oiler structure fastened to said tube and constrained to rotate with said tube, said de-oiler structure having an inlet first face communicating with said volume and an outlet second face connected to the passage formed in said hollow tube; and 
     transmission means between said hollow tube and said shaft for communicating to said hollow tube a speed of rotation V about its axis in such a manner that said speed of rotation V is greater than the speed of rotation v of said rotary shaft.

The present invention relates to a de-oiler system for an aeroengine,and to an aeroengine including such a de-oiler system. In an aeroengine,and in particular in a turbojet, oil flows are circulated towardscertain components, in particular in order to perform lubricationfunctions. After being introduced into members that need to belubricated, the oil is recovered so as to be recycled and thusreinjected once more into the lubrication circuit.

Nevertheless, lubrication circuits are not completely leaktight, andthere are losses that define oil consumption of the engine.

BACKGROUND OF THE INVENTION

The main source of oil leakage is to be found in the system forde-oiling the air from engine enclosures associated with front and rearbearings of the engine: air flows to the bearing enclosures betweenparts that are rotary and stationary, and the air picks up oil, beingsubsequently vented to the outside through a de-oiler system. Increasingthe air/oil separation power of the de-oiler system makes it possible toreduce the oil consumption of the engine or the turbojet, and thus toreduce the cost of operating it.

Accompanying FIG. 1 shows an example of a known de-oiler system mountedin the rear bearing enclosure of a turbojet. This figure shows the rearbearing enclosure 10 and the hollow rotary tube 12 for recovering gasthat comes from the front bearing enclosure. It also showspressurization tubes 14 that enable air to be injected into theenclosure 10 in order to prevent fluid entering into the enclosure.

De-oiling proper is obtained with the help of a centrifugal de-oiler 16of annular shape that is mounted on the axial degassing tube 12. Theinlet face 16 a of the de-oiler 16 is in contact with the oil-laden aircontained in the enclosure 10, while its outlet 16 b communicates withthe axial degassing tube 12. The centrifugal de-oiler 16 is constrainedto rotate with the tube 12. In simplified manner, the de-oiler 16 isconstituted by a plurality of microchannels, e.g. constituted by ahoneycomb structure, with the edges of the inlet face 16 a tending,under the effect of the de-oiler rotating, to remove the oil dropletsthat are sent towards the enclosure 10 while allowing air to passtowards the degassing tube under the effect of the pressure that existsin the enclosure 10. This thus separates the oil from the air, the oilbeing recovered by a pump circuit opening out into the bottom portion ofthe enclosure 10, which circuit is not shown in FIG. 1.

In such a system, the speed of rotation of the de-oiler 16 is naturallydetermined by the speed of rotation of the degassing tube 12. It isfound that with such a system, the rate at which oil is separated fromthe air is significantly less than the target rate, and that this givesrise to increase oil consumption.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the present invention is to provide a de-oiler system foran aeroengine that makes it possible to improve the rate at whichlubricating oil is recycled, i.e. the rate at which oil is separatedfrom air, without significantly complicating the structure, e.g. of therear bearing enclosure of the aeroengine.

According to the invention, to achieve this object, the de-oiler systemfor an aeroengine having a casing defining a volume containing a mixtureof air and oil for processing and a hollow rotary shaft comprising:

a rotary hollow tube distinct from said shaft;

a de-oiler structure fastened to said tube and constrained to rotatewith said tube, said de-oiler structure having an inlet first facecommunicating with said volume and an outlet second face connected tothe passage provided in said hollow tube; and

transmission means between said hollow tube and said shaft forcommunicating a speed of rotation V to said hollow tube about its axisin such a manner that said speed of rotation V is greater than the speedof rotation v of said rotary shaft, whereby the droplets of oilcontained in the air inside the casing are removed towards the casing ofthe inlet face of said de-oiler structure and the processed air iscollected via said passage of the rotary hollow tube.

It can be understood that in the invention the de-oiler structure isdriven at a speed of rotation that is no longer the speed of rotation ofthe hollow rotary shaft, i.e. the degassing shaft, but at a speed ofrotation that can be defined by selecting an appropriate ratio betweenthe speed V and the speed v for optimizing the operation of the de-oilerstructure.

In addition, it can be seen that even though the de-oiler structureconstitutes an additional part, it does not alter the generalorganization of the bearing enclosure that usually constitutes thecasing in which de-oiling is performed.

Preferably, the axes of said hollow tube and of said rotary shaft areparallel. Thus, implementing the transmission is significantlysimplified.

Preferably, said transmission means comprise a first gearwheel mountedon said hollow tube co-operating with a second gearwheel mounted on saidrotary shaft.

Also preferably, said hollow tube passes through the wall of said casingand a labyrinth type gasket is interposed between said hollow tube andthe wall of said casing.

Also preferably, bearings secured to the casing wall are provided, inwhich bearings said hollow tube is mounted to enable it to be centered.

Also preferably, the de-oiler structure is of the metal foam type.

The invention also provides an aeroengine or more particularly anairplane turbojet wherein its de-oiler system is in accordance with theabove-specified characteristics, the de-oiler system preferably beingmounted in the enclosure associated with the rear bearing. It may alsooptionally be mounted in the front bearing enclosure, or indeed betweenthe two enclosures.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention appear better onreading the following description of a preferred embodiment of theinvention, given by way of non-limiting example. The description refersto the accompanying figures, in which:

FIG. 1, described above, shows a prior art de-oiler system mounted inthe rear bearing enclosure of a turbojet;

FIG. 2 is an axial section view of the rear bearing enclosure of aturbojet fitted with a de-oiler system in accordance with the invention;

FIG. 3A is a cross-section view on line A-A of FIG. 2;

FIG. 3B is a cross-section view on B-B of FIG. 2; and

FIG. 3C is a cross-section view on line C-C of FIG. 2.

MORE DETAILED DESCRIPTION

With reference initially to FIG. 2, there follows a description of thegeneral organization of the de-oiler structure in accordance with theinvention, mounted in the rear bearing enclosure 10 of an aeroengine, ormore precisely of a turbojet. In this figure, there can be seen oncemore not only the enclosure 10, but also the rotary hollow axial gasrecovery tube 12 coming from the front bearing enclosure, and air flowis represented by arrows A, while air-oil mixture flow is represented byarrows AH.

The de-oiler structure given overall reference 20 is essentiallyconstituted by a hollow rotary tube 21 having an annular centrifugalde-oiler structure 22 mounted thereon. The hollow tube 21 is preferablymounted in such a manner that its axis XX′ is parallel to the axis YY′of the degassing tube 12. Nevertheless, these axes need not be mutuallyparallel. The hollow tube 21 is mounted in two series of bearings 24 and26, themselves mounted in support structures 28 and 30 secured to therear bearing enclosure. The de-oiler annular structure 22 has an outerinlet face 22 a that is directly in contact with the volume defined bythe rear bearing enclosure 10, and by an inner outlet face 22 b that isconnected to the passage 34 defined by the hollow tube 21. The hollowtube 21 has a first end 21 a that is closed and a second end 21 b thatis open and that enables air to be recovered from the outlet of thede-oiler structure 20. In order to provide sealing relative to thehollow tube 21, labyrinth type gaskets 40 and 42 are mounted firstly onthe outside face of the tube 21 and secondly on the pressurization pipes14.

With reference FIG. 3A, there follows a description of a preferredembodiment of the mechanical transmission between the low pressure gasrecovery shaft 12 and the hollow tube 21 of the de-oiler structure 22.Preferably, the transmission system given overall reference 44 isconstituted by two gearwheels 46 and 48 mounted respectively on theoutside face of the low pressure degassing tube 12 and on the outsideface of the hollow tube 21 of the de-oiler structure. It will beunderstood that by appropriately defining the gearwheels 46 and 48, itis possible to give the hollow tube 21 a speed of rotation V about itslongitudinal axis XX′, which speed is well defined and suitable foroptimizing de-oiling operation. The speed V is greater than the speed vof the hollow shaft 12.

FIG. 3B shows the low pressure shaft 12, the hollow tube 21, and thede-oiler centrifugal annular structure 22 with its inlet face 22 a andits outlet face 22 b.

In FIG. 3C, there can seen once more the low pressure degassing tube 12,and the hollow tube 21, these two hollow tubes being provided with“wipers” 50 and 52 constituting the labyrinth gaskets 40 and morespecifically 42.

In the above description, the de-oiler structure is mounted in the rearbearing enclosure, which corresponds to the best solution economicallyspeaking. Nevertheless, a de-oiler structure could naturally equallywell be mounted in the front bearing enclosure, or indeed in bothenclosures.

1. A de-oiler system for an aeroengine having a casing defining a volumecontaining a rotary shaft and a mixture of air and oil for processing,the de-oiler system comprising: a rotary hollow tube distinct from saidshaft; a de-oiler structure fastened to said tube and constrained torotate with said tube, said de-oiler structure having an inlet firstface communicating with said volume and an outlet second face connectedto the passage provided in said hollow tube; and transmission meansbetween said hollow tube and said shaft for communicating a speed ofrotation V to said hollow tube about its axis in such a manner that saidspeed of rotation V is greater than the speed of rotation v of saidrotary shaft, whereby the droplets of oil contained in the air insidethe casing are removed towards the casing of the inlet face of saidde-oiler structure and the processed air is collected via said passageof the rotary hollow tube.
 2. A de-oiler system according to claim 1,wherein the axes of said hollow tube and of said rotary shaft areparallel.
 3. A de-oiler system according to claim 2, wherein saidtransmission means comprise a first gearwheel mounted on said hollowtube co-operating with a second gearwheel mounted on said rotary shaft.4. A de-oiler system according to claim 1, wherein said hollow tubepasses through the wall of said casing and wherein a labyrinth typegasket is interposed between said hollow tube and the wall of saidcasing.
 5. A de-oiler system according to claim 1, further includingbearings secured to the wall of the casing and in which said hollow tubeis mounted to rotate.
 6. A de-oiler system according to claim 1, whereinsaid shaft structure is in the form of a cylindrical sleeve with itsinlet face being its outer cylindrical face and its outlet face beingits inner cylindrical face.
 7. A de-oiler system according to claim 1,wherein the de-oiler structure is of the metal foam type.
 8. Anaeroengine, including a de-oiler system according to claim 1, mounted inthe enclosure associated with the front and/or rear bearings.